1. Technical Field
The present disclosure relates generally to ball seats for use in oil and gas wells and more specifically to a ball seat having a seat that uses a ratcheting, indexing, or gear-type system to selectively open the sleeve for well fracturing. The present disclosure also relates to a plugging device for use in oil and gas wells and more specifically to a plugging device having a seating shoulder that uses a ratcheting, indexing or gear system to selectively land and shoulder on a ball seat.
2. Related Art
This section of this document introduces various pieces of the art that may be related to or provide context for some aspects of the technique described herein and/or claimed below. It provides background information to facilitate a better understanding of that which is disclosed herein. This is a discussion of “related” art. That such art is related in no way implies that it is also “prior” art. The related art may or may not be prior art. The discussion in this section is to be read in this light, and not as admissions of prior art.
Fracturing is a process that results in the creation of fractures in rocks, being an important industrial process in both oil and gas wells. The technique of fracturing (or “fracking”) is used to increase or restore the rate at which fluids, such as oil, gas or water, can be produced from a reservoir, including unconventional reservoirs such as shale rock or coal beds. Fracturing enables the production of natural gas and oil from rock formations deep below the earth's surface (generally 5,000-20,000 feet or 1,500-6,100 m), At such depth, there may not be sufficient porosity and permeability to allow natural gas and oil to flow from the rock into the wellbore at economic rates. The fracture provides a conductive path connecting a larger area of the reservoir to the well, thereby increasing the area from which natural gas or liquid can be recovered from the targeted formation.
For example, a hydraulic fracture is formed by pumping the fracturing fluid into the wellbore at a rate sufficient to increase the pressure within the hole to a value in excess of the fracture gradient of the formation rock. The pressure causes the formation to crack, allowing the fracturing fluid to enter and extend the crack farther into the formation. Hydraulic fracture stimulation is commonly applied to wells drilled in low-permeability reservoirs.
The location of fracturing along the length of the borehole can be controlled by using ball-activated sliding sleeves (also known as stimulation valves, ball valves, etc.) below and above the region to he fractured. This allows a wellbore (a.k.a., the “borehole”) to be progressively fractured along the length of the bore, without leaking fracture fluid out through previously fractured regions. Piping above the valves admits fracturing fluid and proppant into the working region. These stimulation valves typically use ban seats and plug elements.
Ball seats are generally known in the art. For example, U.S. Letters Pat. No. 7,503,392 (the “'392 patent”), entitled “DEFORMABLE BALL SEAT”, and issued Mar. 17, 2009, to King, et al., portions of which are reproduced herein, discloses apparatuses for restricting fluid flow through a well conduit comprising a housing having a longitudinal bore and a collapsible seat disposed within the bore.
A typical ball seat has a bore or passageway that is partially restricted by a seat. The ball (e.g., drop plug or plug element) is disposed on the seat, preventing or restricting fluid from flowing through the bore of the ball seat and, thus, isolating the tubing or conduit section in which the ball seat is disposed. As the fluid pressure above the ball or drop plug builds up, the conduit can be pressurized for tubing testing or actuating a tool connected to the ball seat (such as setting a packer). Ball seats are also used in cased and open hole completions, liner hangers, fracture systems, flow diverters, flow control equipment and sand control completions and systems.
A ball seat allows a ball to land and make a partial or complete seal between the seat and the ball during pressurization. The contact area between the ball and the inner diameter of the seat provides the seal surface. Generally, the total contact area or bearing surface between the ball and the seat is determined by the outer diameter of the ball and the inner diameter of seat. The outer diameter of the contact area is typically determined by the largest diameter ball that can be transported down the conduit. The inner diameter of the seat is typically determined by the allowable contact stress the ball can exert against the contact area and/or the required inner diameter to allow preceding passage of plug elements or tools, and/or subsequent passage of tools after the plug element is removed, through the inner diameter of the seat.
The seat is usually made out of a metal that can withstand high contact forces due to its high yield strength. The ball, however, is typically formed out of a plastic material that has limited compressive strength. Further, the contact area between the ball and seat is typically minimized to maximize the seat inner diameter for the preceding passage of balls, plug elements or other downhole tools. Therefore, in current systems, as the ball size becomes greater, the contact stresses typically become higher due to the increasing ratio of the cross-section of the ball exposed to pressure compared to the cross-section of the ball in contact with the seat. This higher contact pressure has a propensity to cause the plastic balls to fail due to greater contact stresses.
The amount of contact pressure a particular ball seat can safely endure is a direct function of the ball outer diameter, seat inner diameter, applied tubing pressure and ball strength. Because ball strength is limited as discussed above, the seat inner diameter is typically reduced to increase the contact area (to decrease contact stress). The reduced seat inner diameter requires the ball previously dropped through the seat inner diameter to have a smaller outer diameter to pass through this seat inner diameter. This reduction in outer diameter of previous balls continues throughout the length of conduit until ball seats can no longer be utilized. Therefore, a string of conduit is limited as to the number of balls (and thus ball seats) that can be used which reduces the number of actuations that can be performed through a given conduit string.
Therefore, despite the numerous existing ball valve systems, the current technology only allows for a limited number of valves to be run in the conduit string due to incremental ball size limitations. This limitation also restricts the flow area through the lower valves as the flow area through the seats is minimal, Thus, the need exists for an improved ball valve system that eliminates the requirement for a reduction in ball outer diameter while also using a single ball size to increase the number of valves which may be installed on a given conduit string.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.